A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple (at least two) photonic functions and as such is similar to an electronic integrated circuit. The major difference between the two is that a photonic integrated circuit provides functionality for information signals imposed on optical wavelengths typically in the visible spectrum or near infrared 850 nm-1650 nm. On the PIC, a single polarization is utilized. Any light in the other polarization causes degradation in the performance. Off-chip two of these signals may then be coupled to orthogonal polarization states of the output-fiber. Off-chip optical components are very sensitive to alignment for efficient coupling and meeting the right angle of polarization. An active alignment process is required for high performance. Any reflection from off-chip optical components to the chip further degrades the performance of the PIC.
PICs are well suited to applications in various technologies such as telecommunications. In operation, photonic integrated circuits use optical waveguides to implement network elements or devices, such as optical switches, optical routers, optical couplers and wavelength multiplexers/demultiplexers, for example. Such waveguides, when integrated with a photonic integrated circuit, are typically implemented as solid dielectric light conductors, which are fabricated on a substrate in a very similar fashion as semiconductor integrated circuits are manufactured. Waveguides transmit light around optical circuits and also connect to external optical waveguides, such as optical fibers, typically by direct physical abutment of the fiber with the waveguide. However, in such a configuration, a mode mismatch results between the integrated waveguide and the optical fiber. Specifically, because the difference of the refractive index between the core and cladding of a typical waveguide is higher than that of a typical optical fiber, the optical field is more confined in the waveguide than in the fiber.
Another issue is that the PIC has a preferred polarization state in which its functional blocks operate as intended. However, imperfect fabrication causes transformation of the desired TE mode into the TM mode. Any power in the TM mode will impair the performance of the intended PIC. The ratio of TE and TM is referred to as polarization extinction ratio (PER). Standard polarization combining techniques do not offer a polarization selectivity but introduce additional polarization cross-talk thus further decreasing the PER and with this performance.
Accordingly, there is a need for systems, apparatus, and methods that improve upon conventional approaches including the improved methods, system and apparatus provided hereby.